Conventional automatic wiper controller controls a vehicular wiper according to a detected amount of adhesion water caused by raindrops on a windshield. The automatic wiper controller has a control circuit, an infrared ray sensor, and so on. The infrared ray sensor irradiates an infrared ray toward the windshield and detects the infrared ray reflected on a surface of the windshield. The control circuit detects the amount of the adhesion water by the magnitude of the reflected infrared ray. The control circuit operates using a threshold value for preventing the wiper from operating erroneously by disturbances such as noises, and automatically activates the wiper when the detected amount of the adhesion water exceeds the threshold value.
When the vehicle travels out of a roofed space such as a tunnel and foot of bridge, the driver needs some time to adapt the difference of brightness inside of the roofed space and that outside of the roofed space. If it rains outside the roofed space, the driver's sight outside of the roofed space becomes worse and time required to adapt the difference extends. Thus, it is desirable to activate the wiper as soon as possible when the vehicle travels out of the roofed space into outside space where it rains.
However, the conventional automatic wiper controller activates the wiper after some response time, because the amount of the adhesion water is little immediately after running out of the roofed space and the control circuit determines a precipitation only when the detected amount of the adhesion water exceeds the threshold value.